Here you compare apples and pears ! With the mentioning of "tuning" for the reflex enclosure you implicitely note that it has resonant behaviour.
For the cannon you only take the delay given by the line-length into account but generously overlook the fact that the cannon is resonant as well.
Regards
Charles
Dear Phase Accurate...
As far as I'm aware, the cannon is not a resonant structure per se. It's not like an organ pipe, you're not trying to get an air column to vibrate at a particular frequency, what you're doing is imposing a small delay upon the forward and rear radiation such that they combine positively over a particular passband.
In contrast, a reflex cabinet IS getting the air volume within a fixed volume, tuned by a particular dimension of port to react with the movement of the driver to produce a resonance. This has a pre defined group delay.
I can't see how I'm comparing apples and pears, milliseconds is milliseconds. If a bass cabinets output at 20 hz is going to lag 30ms behind the movement of the bass driver that produces the output, that's 30ms of group delay at that frequency. If a cannon producing a similar wavelength has the pressure wave exit the tube 13ms after the movement of the bass driver that produces the output, that's 13ms group delay.
I don't have the equipment to measure imupulse response and delay. If you do, and have access to the Vifa units I've used and wish to build both a cannon and a reflex cabinet that gives similar output at 20Hz and wish to measure the results and inform us then I'm all ears. Go ahaead. In the absence of measurements I'll assume that a NON resonant cannon imposing nothing more than a small delay upon the output in order to bring the forward and rear radiations into phase has less delay (and therefore, in theory, faster bass) than the equivalent resonant reflex cabinet.
Your first post on this topic claimed that the cannon was analogous to a double chamber bass reflex, (not so, it appears just to be a pair of matched delay lines) and that in your experience Bose used heavily resonant structures to produce low quality bass. With regard to this I'd agree if you're using the acousitmass bandpass subs (I use the word sub with trepidation as they have shocking bleedthrough to midrange freq in my experience) as the benchmark.
The first posts by Kelticwizard lifting parts of a few bose paptents appear to be based around the Bose Wave Radio. In theory the concept is the same as the cannon but in practice it tries to bend physics WAAAAAAY too far in my opinion. Your post, (number 11) shows a folding better than a wave radio but to my eyes signicantly more flawed than the stright Bose acoustic wave cannon (as shown in kelticwizard's post 13).
Your next useful post (no 44) seems to suggest a dipole subwoofer more than anything else.
Posts 46 and 47 (Mr feedback's and your own) start with
"Bose Wave Cannons drone like hell, and sound slow or late or something." (no mention made of actually having heard them)
followed by your
"As expected - when you rely heavily on resonant loading."
Which, as I've already stated I don't believe they are.
Posts 48 and 49 (Mr feedback and youreself again) state that they are power hungry (even though they produce more audible output than the equivalent 1/4 wave pipe or reflex cabinet) and that you'd feed them a sine wave in order to be annoying.
You could always put your basball cap on backwards and do laps of your loacal shopping mall carpark playing old Kriss Kross or New Kids music if you wanted to be annoying.
In defence of Mr feedback, in worst and typical Bose fasion, Bose cheat by making a cannon pipe shorter than it ought to be (12 ft)and then apply a bucketload of bass booost and eq to fix the problem. The fault is in the implementation, not the cannon theory. (As it is with the ridiculously labyrinthine wave radio innards)
As a raw out statement, I simply don't believe that mr feedbacks post 51 is correct. Organ pipes are resonant, the bose cannon is a delay line and functions under similar physics and theory to a 1/4 wave pipe (but in this case both forward AND rear output is delayed.)
Personally, having heard more than a few pretty duff sounding bose products I was outright suprised at the effectiveness of this design. Again, when i compared it to a 1/4 wave pipe and found it was better (more efcient) i was suprised. Maybe after all these years some of that fabled (and much publicised) research has finally resulted in at least one "better sound" product.
I'm not in anyway defeding Bose products in general, i far more a fan of the simple ccts, single drivers, horns, valves and vinyl bent myself but this one seems to work and I don't believe that it ought to be slammed or written off simply because it comes from the house of Bose. (add some umlauts above the "o" and it's German for 'unpleasant") (pronounced "berser" as opposed to "bows")
If i have misunderstood the intent or content of posts by youself or Mr Feedback I sincerely apologise but i got the impression that from the outset you were expecting a crap result and i don't believe that's what has eventuated.
Drew
As far as I'm aware, the cannon is not a resonant structure per se. It's not like an organ pipe, you're not trying to get an air column to vibrate at a particular frequency, what you're doing is imposing a small delay upon the forward and rear radiation such that they combine positively over a particular passband.
In contrast, a reflex cabinet IS getting the air volume within a fixed volume, tuned by a particular dimension of port to react with the movement of the driver to produce a resonance. This has a pre defined group delay.
I can't see how I'm comparing apples and pears, milliseconds is milliseconds. If a bass cabinets output at 20 hz is going to lag 30ms behind the movement of the bass driver that produces the output, that's 30ms of group delay at that frequency. If a cannon producing a similar wavelength has the pressure wave exit the tube 13ms after the movement of the bass driver that produces the output, that's 13ms group delay.
I don't have the equipment to measure imupulse response and delay. If you do, and have access to the Vifa units I've used and wish to build both a cannon and a reflex cabinet that gives similar output at 20Hz and wish to measure the results and inform us then I'm all ears. Go ahaead. In the absence of measurements I'll assume that a NON resonant cannon imposing nothing more than a small delay upon the output in order to bring the forward and rear radiations into phase has less delay (and therefore, in theory, faster bass) than the equivalent resonant reflex cabinet.
Your first post on this topic claimed that the cannon was analogous to a double chamber bass reflex, (not so, it appears just to be a pair of matched delay lines) and that in your experience Bose used heavily resonant structures to produce low quality bass. With regard to this I'd agree if you're using the acousitmass bandpass subs (I use the word sub with trepidation as they have shocking bleedthrough to midrange freq in my experience) as the benchmark.
The first posts by Kelticwizard lifting parts of a few bose paptents appear to be based around the Bose Wave Radio. In theory the concept is the same as the cannon but in practice it tries to bend physics WAAAAAAY too far in my opinion. Your post, (number 11) shows a folding better than a wave radio but to my eyes signicantly more flawed than the stright Bose acoustic wave cannon (as shown in kelticwizard's post 13).
Your next useful post (no 44) seems to suggest a dipole subwoofer more than anything else.
Posts 46 and 47 (Mr feedback's and your own) start with
"Bose Wave Cannons drone like hell, and sound slow or late or something." (no mention made of actually having heard them)
followed by your
"As expected - when you rely heavily on resonant loading."
Which, as I've already stated I don't believe they are.
Posts 48 and 49 (Mr feedback and youreself again) state that they are power hungry (even though they produce more audible output than the equivalent 1/4 wave pipe or reflex cabinet) and that you'd feed them a sine wave in order to be annoying.
You could always put your basball cap on backwards and do laps of your loacal shopping mall carpark playing old Kriss Kross or New Kids music if you wanted to be annoying.
In defence of Mr feedback, in worst and typical Bose fasion, Bose cheat by making a cannon pipe shorter than it ought to be (12 ft)and then apply a bucketload of bass booost and eq to fix the problem. The fault is in the implementation, not the cannon theory. (As it is with the ridiculously labyrinthine wave radio innards)
As a raw out statement, I simply don't believe that mr feedbacks post 51 is correct. Organ pipes are resonant, the bose cannon is a delay line and functions under similar physics and theory to a 1/4 wave pipe (but in this case both forward AND rear output is delayed.)
Personally, having heard more than a few pretty duff sounding bose products I was outright suprised at the effectiveness of this design. Again, when i compared it to a 1/4 wave pipe and found it was better (more efcient) i was suprised. Maybe after all these years some of that fabled (and much publicised) research has finally resulted in at least one "better sound" product.
I'm not in anyway defeding Bose products in general, i far more a fan of the simple ccts, single drivers, horns, valves and vinyl bent myself but this one seems to work and I don't believe that it ought to be slammed or written off simply because it comes from the house of Bose. (add some umlauts above the "o" and it's German for 'unpleasant") (pronounced "berser" as opposed to "bows")
If i have misunderstood the intent or content of posts by youself or Mr Feedback I sincerely apologise but i got the impression that from the outset you were expecting a crap result and i don't believe that's what has eventuated.
Drew
Dear Drew
I apologize if I might have sounded harsh.
I was once interested to build such a thingie as well, thats why I did some thinking about folding (which is of course worse than a stright one and was done out of practical considerations).
In the meantime I am more interested in sytems that are time-aligned and therefore such an apparatus is out of the question.
I was able to listen to a huge stack of them at an open-air cinema event and I wasn't impressed about their sound. Though I have to admit that this might as well be caused by the rest of the system.
Regarding efficiency:If you take the target marked into account then their efficiency is definitely low, compared to REAL P.A. speakers. But for domestic use they are still at the upper end of course.
My mentioning of a neighbour annoying device came from some thinking I did some time ago when I was wondering about how could one build a high-level single-frequency sound source for very low frequencies.
Two 1/4 wave tubes emerging form opposite sides of a chamber and driven by the opposite sides of the cone would do the trick and would furthermore achieve an eight shaped directional characteristic. This is one thing I will once try out if I have the time to waste (I would use some nice RCF 18" woofers).
As to the resonance thing.
I do not know how you come to the conclusion that an undamped tube is non-resonant ?
What the tube actually does is presenting two unterminated waveguides to both sides of your driver's cone. Each one is showing a frequency dependant complex load to your driver (i.e. they act as frequency dependant impedance transformation as it can be done with ordinary cable at RF frequencies).
The combination of the lengths in use allow for a resulting bandpass frequency response (as far as I remember, I was among the first ones within this thread mentioning the actual ratio used and do therefore claim to be not only destructive regarding this topic).
Transformation of this kind comes at a price: Resonance. So the group-delay might be much worse than you assume.
The only acoustical impedance transformer I know that doesn't rely on resonance is a horn, but this comes at the price for even larger size.
Regards
Charles
I apologize if I might have sounded harsh.
I was once interested to build such a thingie as well, thats why I did some thinking about folding (which is of course worse than a stright one and was done out of practical considerations).
In the meantime I am more interested in sytems that are time-aligned and therefore such an apparatus is out of the question.
I was able to listen to a huge stack of them at an open-air cinema event and I wasn't impressed about their sound. Though I have to admit that this might as well be caused by the rest of the system.
Regarding efficiency:If you take the target marked into account then their efficiency is definitely low, compared to REAL P.A. speakers. But for domestic use they are still at the upper end of course.
My mentioning of a neighbour annoying device came from some thinking I did some time ago when I was wondering about how could one build a high-level single-frequency sound source for very low frequencies.
Two 1/4 wave tubes emerging form opposite sides of a chamber and driven by the opposite sides of the cone would do the trick and would furthermore achieve an eight shaped directional characteristic. This is one thing I will once try out if I have the time to waste (I would use some nice RCF 18" woofers).
As to the resonance thing.
I do not know how you come to the conclusion that an undamped tube is non-resonant ?
What the tube actually does is presenting two unterminated waveguides to both sides of your driver's cone. Each one is showing a frequency dependant complex load to your driver (i.e. they act as frequency dependant impedance transformation as it can be done with ordinary cable at RF frequencies).
The combination of the lengths in use allow for a resulting bandpass frequency response (as far as I remember, I was among the first ones within this thread mentioning the actual ratio used and do therefore claim to be not only destructive regarding this topic).
Transformation of this kind comes at a price: Resonance. So the group-delay might be much worse than you assume.
The only acoustical impedance transformer I know that doesn't rely on resonance is a horn, but this comes at the price for even larger size.
Regards
Charles
I could just see someone cutting a hole in their garage wall and aiming a Wave Cannon at a particularly annoying neighbor's house through the wall.
"Hey, neighbor, whatcha doin'?"
"Oh, I'm just cutting a hole for...my bathroom vent fan..."
DrewP: You shoud make sure to keep all the theory you've worked out with regards to the Wave Cannon, so that if anyone asks, you can provide it. Bose might be angry if you make a web page, but you can always work through here.
"Hey, neighbor, whatcha doin'?"
"Oh, I'm just cutting a hole for...my bathroom vent fan..."
DrewP: You shoud make sure to keep all the theory you've worked out with regards to the Wave Cannon, so that if anyone asks, you can provide it. Bose might be angry if you make a web page, but you can always work through here.
Amar Bose understands the patent process really well, or he wouldn't have so many. Not all are completely original, just novel enough not to be obvious with regards to the "prior art."
DrewP: If anything you do might violate the existing patents, just don't try to make any money from it. Reverse engineering or duplication for personal use is fine, but commerce is prohibited by IP law.
ensen.
DrewP: If anything you do might violate the existing patents, just don't try to make any money from it. Reverse engineering or duplication for personal use is fine, but commerce is prohibited by IP law.
ensen.dear Phase Accurate, sorry if I seemed a touch defensive, I'm having a few hassles at work and 3/4 of my project team have just been laid off due to funding cuts while the project deadline remains unchanged at october. The manpower of 18 is more than the manpower of 4 but i shouldn't inflict this on others, I'm sorry.
Although the air mass trapped within the tube may impose a load upon the drive unit I wouldn't classify it as a waveguide anymore than a dipole subwoofer of the slotted type you see on the loudspeakers forum from time to time is a waveguide.
My understanding of the theory was that, precisely like the dipole sub, the extened path to free air on each side of the drive unit was simply there to achieve time delay.
Yes, an air volume in a tube will be resonsant, this is a given but in loudspeaker engineering terms, construction of a resonant system is usually more along the lines of dual chamber ported subs, reflex cabinets and the like.
When faced with a statement such as (paraphrasing here)
"It acts as a dual chamber resonant bandpass sysytem"
I think of crappy acoustimass subs, Kef coupled cavities and the like.
When these are modelled (say in WinISD) and you look at the group delay caused by trying to achive a boost in the freq range due solely to the resonant action of the chambers, then pretty much without fail, for low bass frequencies they are significantly time delayed.
In contrast, although the cannon may well be resonant (a byproduct of its shape) it is not IMO deliberately resonant in order to boost output. the badpass response and boosting of output is achieved by bringing the rear radiation of the cone into phase with the forward radiation of the cone over a particular range of frequencies.
Regarding the efficiency of the Bose system, again I would suspect that this is as a result of less than ideal implementation. (a less than best quality drive unit) i expect that a high efficiency TAD or Beyma unit wth low FS and good excursion would improve things dramatically and, as I stated a while back, they've drastically cut corners in the pipe length and made up for it with EQ where (ideally) the pipe should be longer. Of course, that would make production and shipping costs more and make it harder to install and less unobtrisive but it'd be more effective and elegant from an engineering viewpoint. bose have a long tradition of making up for non ideal implementation with EQ and i feel this is yet another example of the art.
BAM: You can't point just one end of the cannon outside and get it to work, it's the acoustic summing of the output from both ends of the pipe that you hear.
Purplepeople: No plans for commercial production, just one for me and a couple for friends. Not even any labour charges!
(and me a struggling conservator and all!)
Drew
Although the air mass trapped within the tube may impose a load upon the drive unit I wouldn't classify it as a waveguide anymore than a dipole subwoofer of the slotted type you see on the loudspeakers forum from time to time is a waveguide.
My understanding of the theory was that, precisely like the dipole sub, the extened path to free air on each side of the drive unit was simply there to achieve time delay.
Yes, an air volume in a tube will be resonsant, this is a given but in loudspeaker engineering terms, construction of a resonant system is usually more along the lines of dual chamber ported subs, reflex cabinets and the like.
When faced with a statement such as (paraphrasing here)
"It acts as a dual chamber resonant bandpass sysytem"
I think of crappy acoustimass subs, Kef coupled cavities and the like.
When these are modelled (say in WinISD) and you look at the group delay caused by trying to achive a boost in the freq range due solely to the resonant action of the chambers, then pretty much without fail, for low bass frequencies they are significantly time delayed.
In contrast, although the cannon may well be resonant (a byproduct of its shape) it is not IMO deliberately resonant in order to boost output. the badpass response and boosting of output is achieved by bringing the rear radiation of the cone into phase with the forward radiation of the cone over a particular range of frequencies.
Regarding the efficiency of the Bose system, again I would suspect that this is as a result of less than ideal implementation. (a less than best quality drive unit) i expect that a high efficiency TAD or Beyma unit wth low FS and good excursion would improve things dramatically and, as I stated a while back, they've drastically cut corners in the pipe length and made up for it with EQ where (ideally) the pipe should be longer. Of course, that would make production and shipping costs more and make it harder to install and less unobtrisive but it'd be more effective and elegant from an engineering viewpoint. bose have a long tradition of making up for non ideal implementation with EQ and i feel this is yet another example of the art.
BAM: You can't point just one end of the cannon outside and get it to work, it's the acoustic summing of the output from both ends of the pipe that you hear.
Purplepeople: No plans for commercial production, just one for me and a couple for friends. Not even any labour charges!
(and me a struggling conservator and all!)
Drew
Go Aussie, Oy, Oy, Oy.
Hi Drew,
No insult percieved at this end.
My comments re the Bose cannon is that as I have heard them, they are droney and I was never impressed with them, but as you suggest this may be due to the implementation.
I am all for you bringing this experiment to fruition and telling us of your results.
I am a little concened about roof space mounting for your neighbours sake - all that bass is going to radiate, and expect secondary effects like roof tiles rattling.
However I hope that this is a success for you.
Eric.
Hi Drew,
No insult percieved at this end.
My comments re the Bose cannon is that as I have heard them, they are droney and I was never impressed with them, but as you suggest this may be due to the implementation.
I am all for you bringing this experiment to fruition and telling us of your results.
I am a little concened about roof space mounting for your neighbours sake - all that bass is going to radiate, and expect secondary effects like roof tiles rattling.
However I hope that this is a success for you.
Eric.
Fortunately I have a Colourbond steel roof, so no roof tile flapping.
Any sub that went this low would radiate outside the house (the doofy hatchback proof in action again) but unlike phase accurate, deliberate irritation of the neighbours is not my final goal. I'm looking for low end fill, not huge volumes and (as I value my hearing) I don't tend to "crank it" all that much.
Drew
Any sub that went this low would radiate outside the house (the doofy hatchback proof in action again) but unlike phase accurate, deliberate irritation of the neighbours is not my final goal. I'm looking for low end fill, not huge volumes and (as I value my hearing) I don't tend to "crank it" all that much.
Drew
Rattling The Neighbours ?.
I have done a band recording in a poolside room with colourbond roofing that ratttled like hell.
It took a bit of doing with a DAW FFT filter to home in on and remove that rattle but I did it.
I have a friend with a big isobaric sub, and his roof tiles ratttle according to level - he lives out in the sticks so no neighbours to annoy in his case.
Any low bass rumble coming from the neighbours at night can be a real pita in my experience, although this has been from typical modern droney sub boxes.
When I run my system at normal levels, I close all doors and windows to the outside, and when I crank it, I close all internal doors also.
Part of the problem ime is that if the bass is clean and nice, then it natural to run it that bit louder, and without realising the loudness outside and over the fence.
What would happen if you were to make the tube U shaped with both ends radiating into the room ?.
Eric.
I have done a band recording in a poolside room with colourbond roofing that ratttled like hell.
It took a bit of doing with a DAW FFT filter to home in on and remove that rattle but I did it.
I have a friend with a big isobaric sub, and his roof tiles ratttle according to level - he lives out in the sticks so no neighbours to annoy in his case.
Any low bass rumble coming from the neighbours at night can be a real pita in my experience, although this has been from typical modern droney sub boxes.
When I run my system at normal levels, I close all doors and windows to the outside, and when I crank it, I close all internal doors also.
Part of the problem ime is that if the bass is clean and nice, then it natural to run it that bit louder, and without realising the loudness outside and over the fence.
What would happen if you were to make the tube U shaped with both ends radiating into the room ?.
Eric.
Hi Drew
One fact that keeps me from looking at the cannon as some sort of dipole is the fact that the flattest response is achieved when the distance between listening position and both ends of the line are the same. If you listen to a dipole speaker from the side you will definitely have an SPL minimum.
Furthermore it is possible to use different length ratios than Bose uses that allow a more peaky response but further improved efficiency (2 dB approx). I have a JAES article dealing with horn modeling where this is discussed as well. There the arrangement is called "resonant tube system".
I do however agree that the total mass of the driver will be affected. As this would definitely decrease the efficiency, one has to assume that there is also another mechanism in effect than just increasing mass on the driver (i.e. one that is achieving frequency dependant improvement of loading).
But the mass-increase might be one reason that Bose doesn't use a longer cannon. If you have larger cannons and even need more of them (to achieve the same SPL) then you will end up with a less profitable solution.
I completely agree that Bose often uses the principles that impresses many people the most with the least effort on the technical side.
But having professional users in mind a manufacturer has to take care of their profit as well, if both want to stay in business. P.A. speakers that go down to 30 Hz are definitely available, but quite rare simply due to economical reasons.
The homebuilder however may use cannons, TMLs, horns and whatever as insanely large as he likes and is willing to pay for (and the SO permits ).
Regards
Charles
One fact that keeps me from looking at the cannon as some sort of dipole is the fact that the flattest response is achieved when the distance between listening position and both ends of the line are the same. If you listen to a dipole speaker from the side you will definitely have an SPL minimum.
Furthermore it is possible to use different length ratios than Bose uses that allow a more peaky response but further improved efficiency (2 dB approx). I have a JAES article dealing with horn modeling where this is discussed as well. There the arrangement is called "resonant tube system".
I do however agree that the total mass of the driver will be affected. As this would definitely decrease the efficiency, one has to assume that there is also another mechanism in effect than just increasing mass on the driver (i.e. one that is achieving frequency dependant improvement of loading).
But the mass-increase might be one reason that Bose doesn't use a longer cannon. If you have larger cannons and even need more of them (to achieve the same SPL) then you will end up with a less profitable solution.
I completely agree that Bose often uses the principles that impresses many people the most with the least effort on the technical side.
But having professional users in mind a manufacturer has to take care of their profit as well, if both want to stay in business. P.A. speakers that go down to 30 Hz are definitely available, but quite rare simply due to economical reasons.
The homebuilder however may use cannons, TMLs, horns and whatever as insanely large as he likes and is willing to pay for (and the SO permits
).Regards
Charles
Agreed, the cannon is not a dipole but the time delay aspect of the structure is similar to the time delay related to baffle width, or front to rear distance.
Changing the pipe ratios would alter how much and at what requency the come in and out of phase.
It seems that the 1/4 : 3/4 ratio gives a broader passband with some gain. no doubt other ratios would peak differently and have a differing passband shape.
does the mass loading imposed on the driver by the air column have the effect of lowering Fs (as if the driver diaphragm was heavier)?
Changing the pipe ratios would alter how much and at what requency the come in and out of phase.
It seems that the 1/4 : 3/4 ratio gives a broader passband with some gain. no doubt other ratios would peak differently and have a differing passband shape.
does the mass loading imposed on the driver by the air column have the effect of lowering Fs (as if the driver diaphragm was heavier)?
After reading through Bose's patent many times I have come up with the following on how Bose designs their wave products: 1. Choose the speed of sound travelling within the pipe
2. Divide the speed by four.
3. Take that value and divide it by the desired cut-off frequency.
Determining the cross-sectional area (ATCR-method (?)):
Ac=effective cone area of driver.
At=Cross-sectional area.
ATCR= constant (below 0.5=Peaky response, 0.5=smooth response, above 0.5=peaky response) *Note: a value of 0.45, for example, may be chosen if a larger Bl factor is chosen {BL relationship yet to be figured out}.
ATCR=At/Ac.
Using math, you can find the diamater or, Length and width values for the pipe after determning the At.
What about the pipe in front of the driver? Well, that is simply one third the length of the pipe behind the driver. Why? It produces a phase reversal at certain frequencies where the rear pipe also reverses the phase. The two waves meet and add up as to increase the effective response range of the pipe.
I haven't tried this method yet, though, I will be soon as I build my surround TL's.
2. Divide the speed by four.
3. Take that value and divide it by the desired cut-off frequency.
Determining the cross-sectional area (ATCR-method (?)):
Ac=effective cone area of driver.
At=Cross-sectional area.
ATCR= constant (below 0.5=Peaky response, 0.5=smooth response, above 0.5=peaky response) *Note: a value of 0.45, for example, may be chosen if a larger Bl factor is chosen {BL relationship yet to be figured out}.
ATCR=At/Ac.
Using math, you can find the diamater or, Length and width values for the pipe after determning the At.
What about the pipe in front of the driver? Well, that is simply one third the length of the pipe behind the driver. Why? It produces a phase reversal at certain frequencies where the rear pipe also reverses the phase. The two waves meet and add up as to increase the effective response range of the pipe.
I haven't tried this method yet, though, I will be soon as I build my surround TL's.
I built two of these during the summer of 2001.
I had heard rumors that Bose had developed amazing
bass using a series of acoustic labyrinths (a complicated system
of "sound caves").
I then saw a 30-minute infomercial on the "Bose Acoustic Wave System".
I, too, found the Bose patent on the web (United States Patent 4,628,528). Lacking a suitable viewer, I had no pictures / graphics. (but I had seen the ad showing the folded tube technology).
My initial design was very complex -- thinking that many
folds in the tube might be key.
I quickly realized that I could not possibly build such a
design however (being a hack).
After many iterations I came up with a simpler design essentially
the same as here (see phase_accurate's) -- "great minds think alike"
I used Georgia Pacific 3/4" void free plywood, 2" deck screws, and
Gorilla (polyurethane) glue (my reasoning -- ww.gatorboats.com -- see FAQ ).
I doubled up to 1.5" on the piece where the 14" driver is attached. Wherever there is a fold I used 45 degree 7" corner braces from excess 3/4" stock. I glued all connecting surfaces
and screwed every 3".
I know this flies in the face of conventional wisdom
(source: David Dlugos' (outstanding) www.t-linespeakers.org
-- see "Perfectionist Audio" under "coffin" design)).
But it IS very solid -- perhaps because there is a bed
and people on top of it holding it down.
;-)
After two years of living with it my wife still says it is the
best bass she has ever heard -- open, airy, and DEEP.
I originally built four 15" x 15" x 30" reflex 3/4" MDF
enclosures with lots of bracing and active equalization to get
same effect. The WAF was low because they took up
lots of space in the room.
Now I am getting a FULL OCTAVE of deeper bass from only two, and they are hidden under the bed (with a much more open and airy sound). Ironically, the bed does NOT shake during special effects -- the mattress absorbs the vibrations.
Pink Floyd, organ, classical, and special effects are AWESOME.
(so is all the other stuff except for Moody Blues, Lenny Kravits,
and Savage Garden -- their stuff is mixed with WAY too much bass).
There is no sound at 10hz, -9db at 15hz, -3db at 18hz, and then fairly flat from 20hz to 80hz where it crosses over to six JBL HLS 610s.
long tube: 15' (18hz)
short tube: 5' (55hz)
tube area: 121.5" (9" x 13.5")
ATCR: 1.07 (JBL LE14a cone area (6*6*pi()))
driver: JBL LE14a (Fs=28hz)
taper: none
stuffing: none
equalization none
(NOTE: The Bose patent claims an optimum ATCR of .5 for
flatest response -- I went with an ATCR of 1 and no
stuffing just like thier Acoustic Cannon. See Jon Risch's TL design guidelines at www.t-linespeakers.org.)
A frequent question -- "why so big?"
Per unit of energy there is 1000 times as much distortion at 20hz
as there is at 20 khz. Subs need to be big.
It is claimed that the Bose Acoustic Cannon is the sonic equivalent to a 250 sq ft corner horn (see www.cardhouse.com/x09/wave.htm).
This the effect I was going for and after two years I am still very happy with the result.
Oh yeah, it was a couple of hundred bucks.
I had heard rumors that Bose had developed amazing
bass using a series of acoustic labyrinths (a complicated system
of "sound caves").
I then saw a 30-minute infomercial on the "Bose Acoustic Wave System".
I, too, found the Bose patent on the web (United States Patent 4,628,528). Lacking a suitable viewer, I had no pictures / graphics. (but I had seen the ad showing the folded tube technology).
My initial design was very complex -- thinking that many
folds in the tube might be key.
I quickly realized that I could not possibly build such a
design however (being a hack).
After many iterations I came up with a simpler design essentially
the same as here (see phase_accurate's) -- "great minds think alike"
I used Georgia Pacific 3/4" void free plywood, 2" deck screws, and
Gorilla (polyurethane) glue (my reasoning -- ww.gatorboats.com -- see FAQ ).
I doubled up to 1.5" on the piece where the 14" driver is attached. Wherever there is a fold I used 45 degree 7" corner braces from excess 3/4" stock. I glued all connecting surfaces
and screwed every 3".
I know this flies in the face of conventional wisdom
(source: David Dlugos' (outstanding) www.t-linespeakers.org
-- see "Perfectionist Audio" under "coffin" design)).
But it IS very solid -- perhaps because there is a bed
and people on top of it holding it down.
;-)
After two years of living with it my wife still says it is the
best bass she has ever heard -- open, airy, and DEEP.
I originally built four 15" x 15" x 30" reflex 3/4" MDF
enclosures with lots of bracing and active equalization to get
same effect. The WAF was low because they took up
lots of space in the room.
Now I am getting a FULL OCTAVE of deeper bass from only two, and they are hidden under the bed (with a much more open and airy sound). Ironically, the bed does NOT shake during special effects -- the mattress absorbs the vibrations.
Pink Floyd, organ, classical, and special effects are AWESOME.
(so is all the other stuff except for Moody Blues, Lenny Kravits,
and Savage Garden -- their stuff is mixed with WAY too much bass).
There is no sound at 10hz, -9db at 15hz, -3db at 18hz, and then fairly flat from 20hz to 80hz where it crosses over to six JBL HLS 610s.
long tube: 15' (18hz)
short tube: 5' (55hz)
tube area: 121.5" (9" x 13.5")
ATCR: 1.07 (JBL LE14a cone area (6*6*pi()))
driver: JBL LE14a (Fs=28hz)
taper: none
stuffing: none
equalization none
(NOTE: The Bose patent claims an optimum ATCR of .5 for
flatest response -- I went with an ATCR of 1 and no
stuffing just like thier Acoustic Cannon. See Jon Risch's TL design guidelines at www.t-linespeakers.org.)
A frequent question -- "why so big?"
Per unit of energy there is 1000 times as much distortion at 20hz
as there is at 20 khz. Subs need to be big.
It is claimed that the Bose Acoustic Cannon is the sonic equivalent to a 250 sq ft corner horn (see www.cardhouse.com/x09/wave.htm).
This the effect I was going for and after two years I am still very happy with the result.
Oh yeah, it was a couple of hundred bucks.
efficiency
How efficient is the cofiguration as compared to say sealed box, for instance, at the driver's Fs (18 Hz?) ?
Also, am I to understand that you built this design as a labyrinthed rectangular prism as opposed to the straight pipe design that was being discussed?
Really neat to see someone has actually done this!
How efficient is the cofiguration as compared to say sealed box, for instance, at the driver's Fs (18 Hz?) ?
Also, am I to understand that you built this design as a labyrinthed rectangular prism as opposed to the straight pipe design that was being discussed?
Really neat to see someone has actually done this!
Thank you for the encouragement. It is always nice to hear.
Regarding efficiency, I do not currently have testing equipment here except for my ears.
:-|
I believe, however, that the only thing more efficient than an unstuffed tuned pipe (Dr. Amar Bose's Acoustic Cannon) is a horn loaded sub.
Horns are much more complicated and expensive to build, however (see: http://www.servodrive.com/basstech7.html, http://www.klipsch.com/product/product.aspx?cid=2, http://www.carfrae.com/pages/frameset.html for outstanding examples IMO). Horns also need to be HUGE to go below 20hz.
Regarding efficiency, I do not currently have testing equipment here except for my ears.
:-|
I believe, however, that the only thing more efficient than an unstuffed tuned pipe (Dr. Amar Bose's Acoustic Cannon) is a horn loaded sub.
Horns are much more complicated and expensive to build, however (see: http://www.servodrive.com/basstech7.html, http://www.klipsch.com/product/product.aspx?cid=2, http://www.carfrae.com/pages/frameset.html for outstanding examples IMO). Horns also need to be HUGE to go below 20hz.
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